MONROE, Conn. -- Classes resumed today for the students of Sandy Hook Elementary School for the first time since last month’s massacre in Newtown, where a gunman killed 20 first-graders and six educators.

With their original school still being treated as a crime scene, the more than 400 students are attending classes at a refurbished school in the neighboring town of Monroe. Law enforcement officers have been guarding the new school, and by the reckoning of police, it is “the safest school in America.”

The school district said parents who want to be close to their children are welcome to visit and stay in classrooms or an auditorium throughout the day. Parents were encouraged to have their children take the bus to help them return to familiar routines.

Still, Newtown Superintendent Janet Robinson said officials will do their best to make the students feel at ease.

“We will go to our regular schedule,” she said. “We will be doing a normal day.”

On Wednesday, the students and their families were welcomed at an open house at their new school, which was formerly the Chalk Hill Middle School in Monroe but renamed as the Sandy Hook Elementary School. Students received gift boxes with toys inside and shared joyful reunions with teachers.

One father, Vinny Alvarez, took a moment to thank his third-grade daughter’s teacher, Courtney Martin, who protected the class from a rampaging gunman by locking her classroom door and keeping the children in a corner.

“Everybody there thanked her in their own way,” he said.

The gunman, Adam Lanza, also killed his mother at the home they shared in Newtown before driving to the school and gunning down 26 people, including the school’s principal. Lanza fatally shot himself as police arrived. Police haven’t released any details about a motive.

Numerous police officers on Wednesday guarded the outside of the Monroe school, which is about 7 miles from the old school, and told reporters to stay away.

“I think right now it has to be the safest school in America,” Monroe police Lt. Keith White said.

Teachers attended staff meetings at the new school on Wednesday morning and were visited by Gov. Dannel P. Malloy before the open house, White said.

Robinson said Chalk Hill School has been transformed into a “cheerful” place for the surviving students to resume normal school routines. She said mental health counselors continue to be available for anyone who needs them.

During the open house, Alvarez said his 8-year-old daughter also got to pick out a stuffed animal to take home from the school library.

“I’m not worried about her going back,” he said of his daughter Cynthia. “The fear kind of kicks back in a little bit, but we’re very excited for her and we got to see many, many kids today. The atmosphere was very cheerful.”

Several signs welcoming the Sandy Hook students to their new school were posted along the road leading to the school in a rural, mostly residential neighborhood. One said “Welcome Sandy Hook Elementary Kids,” while a similar sign added “You are in our prayers.”

Teams of workers, many of them volunteers, prepared the Chalk Hill school with fresh paint and new furniture and even raised bathroom floors so the smaller elementary school students can reach the toilets. The students’ desks, backpacks and other belongings that were left behind following the shooting were taken to the new school to make them feel at home.